Construction of gas-filled tubes, particularly shielding



Nov.

13, 1956 H. J, PRAGE'R ET AL 2,770,751

CONSTRUCTION OF GAS-FILLED TUBES PARTICULARLY SHIELDING Filed Feb. 27, 1953 INVENTORS F 4 WMJJMPPMA? 6 j Mann-0022755341:-

HZM a JTTORNIE) United States Patent CONSTRUCTION OF GAS-FILLED TUBES, PARTICULARLY SHIELDING Hans John Prager, Maplewood, and William Curtiss Dale, Basking Ridge, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application February 27, 1953, Serial No. 339,202

7 Claims. (Cl. 313-193) This invention relates to gas discharge devices and particularly to gas discharge devices of the thyratron type.

Gas discharge tubes, such as thyratrons, are designed and intended to furnish, and control, electrical conduction through gases. These discharges can be properly controlled only when confined to a space bounded by elements designed to enclose these discharges. However, to completely control these discharges, it is also necessary to prevent unwanted, spurious discharges external to the enclosed space but still inside the envelope by providing suitable shielding of the elements extending beyond the enclosed space. This invention deals with shielding elements external the desired discharge space in gas discharge devices and particularly with the shielding of elements that are normally at anode potential from elements at cathode potential. Such element usually comprise protruding ears, connectors, and lead-in wires.

In the usual gas discharge devices of the thyratron type under consideration herein, shielding of the elements that are normally at anode potential is comparatively simple because of the large area between the various ele ments that are external to the desired discharge space. However, shielding of these elements in miniature, or sub miniature, gas discharge devices of this type is more complicated due to the fact that the spacing between electrodes is less and, the envelope is relatively small thus requiring smaller shielding elements.

The problems encountered in shielding the anode ears that extend above the tube insulating spacers in a gas discharge device are also complicated by the size of the miniature or subminiature type of device. One of the many problems encountered in constructing the electrode extensions above the tube insulating spacer, or mica, is the fact that certain types of miniature or subminiature thyratrons utilize a blocking grid rod that is normally connected to the control electrode structure. Due to the size of the device, it is difficult to obtain a connection inside the tube envelope for this blocking grid wire that will be conducive to rapid manufacturing techniques. Another problem encountered in gas discharge devices is that shielding should be carried close to the envelope walls to eliminate the possibility of arc-back by eliminating the long path for the electrons and thus eliminating long path discharges.

It is therefore an object of this invention to provide a new and improved structure for shielding electrode ends that extend beyond the active discharge space in a gas tube.

It is a further object of this invention to provide a metallic shield for the electrode ends that provides improved mechanical strength.

It is a still further object of this invention to provide a structure that is substantially more stable, and able to withstand the voltages utilized, as well as temperature cycling, to the end that failure, because of cracked envelopes and stems is substantially reduced.

It is a still further object of this invention to provide a subminiature type of discharge device that is not only mechanically and electrically stable but also is adapted to be readily produced by rapid mass production techniques.

It is a still further object of this invention to provide a new and improved structure for a subminiature type of discharge device that provides adequate space for welding the anode to the anode lead-in conductor after cage assembly.

These and other objects have been accomplished in accordance with the general aspects of this invention by providing a gas discharge device of the miniature or subminiature type having a gas filled envelope. Within the envelope a metallic shield is provided which normally comprises a thin formed piece of metal intermediate the anode lead-in conductor and the remaining lead-in conductors beneath the bottom insulating spacer. The shield is arranged so that the shield extends from the bottom insulating spacer to the envelope stern, and across the inside of the envelope, at the point of shielding. In order to provide mechanical strength and also an electrical connection, this shield is normally connected to one of the various lead-in wires. Above the upper insulating spacer there is provided a substantially U-shaped metal shield that provides shielding of the upper anode cars from the other electrode ends, as well as providing a support for a third insulating spacer. A blocking grid rod is connected to the closed portion of the U-shaped shielding member to avoid the use of additional lead-in connections. Due to the shape and location of the shields, long path discharges are eliminated from both ends of the electrode structure. a

The novel features that are believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself will best be understood by reference to the following descriptions taken in connection with the accompanying single sheet of drawings wherein like reference numerals refer to similar elements throughout the several views and in which:

Figure l is an elevational view, partially in section, of the subminiature gas discharge device embodying the present invention;

Figure 2 is an enlarged cross-sectional view taken along line 22 of Figure 1 and shows the electrode arrangement in this region;

Figure 3 is an enlarged cross-sectional view taken along line 3--3 of Figure l and shows the electrode arrange ment inside the desired discharge space; and

Figure 4 is an enlarged cross-sectional bottom view taken along line 4-4 of Figure 1 showing the shielding of the lead-in conductor in this region in accordance with the present invention.

Referring now to the drawings in more detail, there is shown in Figures 1 through 4 thereof, various views of a preferred embodiment of a gas discharge device constructed in accordance with this invention. The gas discharge device, or tube, shown is commonly referred to as the subminiature size. However, the invention is also applicable to similar gas discharge devices regardless of size. The device includes a tubular envelope 10, having an inner diameter of about 300 mils, that. is closed at one end by a stem 11. The electrode assembly within the envelope l0, referring specifically to Figures 1 and 3, comprises an elongated fiat anode 12 spaced from a eylindrical cathode 13 which is energized by heater 14. A combined control grid and shielding grid 15, of U-shape cross section, partly surrounds the cathode 13, and has side walls defining a passageway 16 through which a gas discharge is to pass. A blocking grid 17, which may be in the form of a rod, is mounted in registry with the passageway in. The electrodes are supported between insulating spacers 18, and 19. The insulating spacers 18 and 19 may be made of any type of insulating material such as mica. The end portions of the electrodes, and the blocking grid rod 17, extend through apertures in insulating spacers 18 and 19 and project beyond the insulating spacers 18 and 19.

The passageway 16 defined by the side walls of the grid 15 has a length in the direction from the cathode to the anode of 75 mils and a width of 30 mils to provide a blocking field of desired length and concentration. The overall width of the grid 15 is 220 mils.

The sheet metal anode 12 has a width of 40 mils and is spaced 200 mils from the center of cathode 1.3. The spacing between anode 12 and the adjacent portions of grid 15 is 25 mils.

The cathode 13 has a diameter of 30 mils while the blocking grid rod 17 has a diameter of 25 mils. The center of the blocking grid rod 17 is spaced 45 mils from the center of the cathode.

The inner diameter of envelope is 300 mils and insulating spacers 18 and 19 also have a diameter of 300 mils for snugly engaging the inner walls of the envelope. The envelope contains Xenon gas at a pressure of about 800 microns. It should be understood that other ionizable mediums and pressures may be utilized.

From the foregoing dimensions and space values, it should be noted that cathode 13 is spaced 30 mils from the side of grid 15 adjacent thereto, and that the blocking grid rod 17 has a diameter about equal to the width of passageway 16 formed by grid 15. This spacing between the cathode 13 and grid 15 is sufiicient to prevent shorts between these electrodes when the grid 15 is energized with a positive voltage. The relation of the diameter of blocking grid rod 17 and width of the passageway 16 is such as to effectively shield the cathode from direct or rectilinear communication with the anode 12 which is of great advantage when the tube is non-conducting. When the tube is conducting, the grid and blocking grid provide a tortuous or winding path for the discharge.

Referring now to Figures 1 and 2 there is shown the upper end of the electrode structure. Cathode 13 extends above insulating spacer 19. Blocking grid 17 also extends through insulating spacer 19 and is preferably connected to a shielding member 2%) that extends between insulating spacer 19 and insulating spacer 21. The shape of shielding member 29 permits a connection between shielding member 24) and the extension of blocking grid rod 17, otherwise an additional lead-in connection would be necessary. The grid 15 has four extensions 15' that extend through insulating spacer 19 and are connected to the shielding member 2b. The grid extensions 15 and shielding member 20 are preferably crimped together due to the small size of the device. The grid extensions 15' also extend through insulating spacer 21. The anode 12 extends above insulating spacer 19 as is shown.

The shielding member 20 supports an insulating spacer 21 which in turn supports a getter loop 22 that is connected to the uppermost ends of the grid extensions 15'. The shielding member 2% is arranged so that it shields the anode 12 extension, or car, from the cathode extension within this area. The shielding member 2% is substantially tJ-shaped in order to give adequate mechanical support to the insulating spacer 2.1 and also to increase the distance of an electron path between the anode 12 and the other electrodes and thus increase the arc-back voltage in accordance with Paschens law. The shielding member 2b may be a thin metallic piece of any suitable metal.

Referring now to Figures 1 and 4, the bottom section of the discharge device 10 comprises the extensions for each of the electrodes and for blocking grid member 17 that extend through insulating spacer 18. Each of the electrodes has an individual lead-in connection 23 that extends through the envelope ltd in the usual manner. intermediate the anode lead-in and the cathode lead-in is located a. metallic shielding member 24. The metallic shielding member 24 extends from the insulating spacer 18 to the bottom of the envelope 10, and substantially from closely adjacent to one side of the envelope 10 to closely adjacent to the other side thereof. The shielding member 24 is made of a thin electrical conductive material, preferably metal, and is so dimensioned and positioned that it adequatelyshields the anode lead-in from the cathode and heater lead-ins. The shielding member 24 provides mechanical support and, when desired, electrical connection to the grid 15, if the shield is connected to the grid lead-in as is shown. Furthermore, theshield has the particular advantage of preventing spurious electrical discharges or even breakdowns or arc-overs between the anode and structure and the other electrode ends.

From the foregoing, it is apparent that by utilizing member 24 the need for the dielectric insulating pantlegs, heretofore used, has been avoided. Thus, with the anode mounted in an electrode cage assembly it is now possible to weld the anode lead-in to the anode by reason of the additional space made available. Furthermore, the percentage of tube failures due to cracked stems, and tubing, caused by arc-over between the anode lead and the cathode, is substantially reduced. In fact, tube failure because of such arc-over is virtually eliminated during operation within the maximum tube ratings.

It is believed obvious that though there is shown only one specific embodiment of the invention, an invention is subject to wide variations and modifications of size, shape, and arrangement without departing from the spirit of the invention. It is therefore intended to cover all such variations and modifications which come within the scope of the appended claims.

We claim:

1. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart insulator members Within said-envelope, a cathode,

a control electrode and an anode supported in spaced relationship between said insulator members, said electrodes extending through both of said insulator members, a different lead-in conductor connected to one of the extended portions of each of said electrodes and sealed through said envelope, a metallic member intermediate the leadin conductor for said anode and the lead-in conductor for said cathode and extending from one of said insulator members substantially to said envelope, a third insulator member, a U-shaped metallic member extending from the other of said insulator members to said third insulator member and intermediate the other extended portion of said anode and the other extended portion of said cathode.

2. A gas discharge device as in claim 1 wherein each of said metallic members is connected to respective extended portions of said control electrode.

3. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart insulator members within said envelope, a cathode and an anode spaced from said cathode, a sheet metal grid having walls defining a recess receiving said cathode and additional walls defining an elongated passageway between said cathode and anode and in registry therewith, a blocking grid adjacent said cathode in said recess and disposed between said cathode and said anode, said electrodes being supported intermediate said pair of insulator members and extending therethrough, a different lead-in conductor for each of said electrodes and each connected to one lOf said electrodes adjacent one of said insulator members, a metallic plate extending from said one of said insulator members to said envelope intermediate the lead-in conductor for said anode and the lead-in conductor for said cathode, said metallic plate substantially extending across the inside of said envelope and being connected to said grid, a third insulator member, a substantially U-shaped metallic member extending and lying parallel and between the other of said insulator members and said third insulator member, and said U- shaped metallic member being connected to said grid and said blocking grid.

4. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of insulating disc members within said envelope and extending transversely of said envelope, a group of electrodes including an anode supported in spaced relation by said insulating members, a. plurality of lead-in conductors extending through one end of said envelope and individual connections between the ends of each of said electrodes and one of said conductors, a metallic plate extending from one of said insulating member-s to said end of said envelope intermediate the anode lead-in conductor and tne cathode lead-in conductor, a third insulating disc member extending transversely :of said envelope, a U- shaped metallic plate extending from the other one of the first mentioned insulating disc members to said third insulating member and intermediate the other end of said anode and the other end of said cathode.

5. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced insulating disc members within said envelope, a group of electrodes including an anode supported in spaced relation by and between said insulating disc members, a plurality of lead-in conductors extending through one end of said envelope and individual connections between one end of each of said electrodes and one of said conductors, a metallic plate extending from one of said insulating disc members to said one end of said envelope, said metallic plate being closely spaced from said envelope walls and positioned between the lead-in connected to the anode and the lead-in connected to said cathode for preventing discharges between the lead-ins of said electrodes, a third insulating disc member, and a substantially U-shaped metallic shielding member lying parallel and between the other one of said pair of insulating disc members and said third insulating disc member, said U-shaped metallic member being intermediate the other end of said anode and the other end of said cath ode for preventing spurious discharges therebetween.

6. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, first, second, and third parallel spaced apart insulator disc members extending transversely of said envelope, a cathode electrode and an anode electrode spaced from said cathode, a sheet metal grid electrode having walls defining a recess receiving said cathode and additional walls defining an elongated passageway between said cathode and said anode and in registry therewith, a blocking grid electrode adjacent said cathode and in said recess and disposed between said cathode and said anode, said electrodes being supported intermediate said first and said second insulator disc members and extending therethrough, lead-in conductors for said electrodes and each connected to one :of said electrodes adjacent said first insulator disc member, a metallic shielding plate extending from said first insulator member to said envelope intermediate the lead-in conductor for said anode and the lead-in conductor for said cathode, said shielding plate extending substantially across the inside of said envelope and. being connected to an extension of said grid, and a substantially U-shaped metallic shielding member lying parallel and between said second and said third insulator disc members and intermediate the extension of said anode and the extension of said cathode, said blocking grid being connected to the closed portion of said U-shaped shielding member.

7. A gas discharge device comprising a sealed envelope 'having an ionizable medium therein, a pair of insulating members spaced apait within said envelope, the cathode electrode, a blocking grid electrode, a control electrode, and an anode supported in spaced relationship in the order named and between said insulating members, said electrodes extending through at least one of said insulating members, a third insulating member, a Ushaped shield extending from said one of said insulating members to said third insulating member and intermediate the extended portion of said anode and the extended portion of said cathode, and said blocking grid being connected to said shield.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,800 Jordan Mar. 14, 1939 2,185,852 Klopprogge Jan. 2, 1940 2,516,675 Carne July 25, 1950 2,660,685 Johnson Nov. 24, 1953 2,688,710 Webster Sept. 7, 1954 

